Canning season is well underway. All the work and patience of gardening is paying off in delicious foods to eat all winter long. Canning foods has a long history. In 1679, French physicist Denis Pepin developed a pressure cooker he called a digester. Pressure cooking uses high pressure steam in a sealed vessel. In a sealed pressure cooker, as the water boils the steam trapped in the cooker raises the pressure and the boiling point of water increases. The pressure results in super-heated water. The high heat of the cooker kills pathogens that cause food poisoning. Over the next three centuries experiments continued in the development of pressure cookers. In 1905, in the U.S., the National Presto Industries developed 50 gallons pressure cookers for canneries and 30 gallons pressure cookers for hotels. By 1915, they were manufacturing 10 gallons pressure cookers for home use. In 1917, The U.S. Department of Agriculture determined that pressure canning was the only safe way to can low acid foods. This 1918 pressure cooker came from professor Lida Burrill, an Extension Nutritionist who did research at South Dakota State University from 1950 to 1965.